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Artigos de revistas sobre o assunto "Modèle pseudopotential"
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Chen, Rui, Jiaolian Luo, Anqi Yang, Zhenyu Xie, Ashraf Y. Elnaggar, Baosheng Liu, Salah M. El-Bahy e Zhanhu Guo. "Electronic structure and delithiation mechanism of vanadium and nickel doped Li2MnPO4F cathode material for lithium-ion batteries". Journal of Materials Science: Materials in Electronics 35, n.º 19 (julho de 2024). http://dx.doi.org/10.1007/s10854-024-13069-3.
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AbstractThis study calculates the energy band structure and density of states of Lithium manganese fluorophosphate (Li2MnPO4F, a lithium transition metal phosphate compounds) using the first-principles plane-wave pseudopotential approach within the density-functional theory. The model of Li2M0.5Mn0.5PO4F (M = V, Ni) with transition metal doped Mn sites is constructed by using the CASTEP module. The calculation findings indicate that the transition metal doping can regulate the energy band structure of the intrinsic system, and Li2MnPO4F makes the band gap decrease, and the volume increase with the Li ions of being deintercalated, and the electrons can be readily stimulated from the valence band to the conduction band. The findings indicate that Li2MnPO4F is a favorable cathode material for high-voltage lithium ion batteries (LIBs). The introduction of vanadium (V) and nickel (Ni) doping reduces the band gap, facilitating an easier excitation of electrons from the valence band to the conduction band. This study provides a theoretical study of new cathode materials for high performance LIBs.
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Bolívar-Pineda, Lina M., Carlos Uriel Mendoza-Domínguez e Vladimir A. Basiuk. "Adsorption of lanthanide double-decker phthalocyanines on single-walled carbon nanotubes: structural changes and electronic properties as studied by density functional theory". Journal of Molecular Modeling 29, n.º 5 (26 de abril de 2023). http://dx.doi.org/10.1007/s00894-023-05557-w.
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Abstract Context Molecular modeling of carbon nanotubes and lanthanide double-decker phthalocyanines hybrids is challenging due to the presence of 4f-electrons. In this paper, we analyzed the trends in structural changes and electronic properties when a lanthanide (La, Gd, and Lu) bisphthalocyanine molecule is adsorbed on the surface of two single-walled carbon nanotubes (SWCNTs) models: armchair and zigzag. The density functional theory (DFT) computations showed that the height of bisphthalocyanines complexes (LnPc2) when adsorbed on a nanotube (LnPc2+SWCNT) is the structural feature which is most affected by the nanotube model. The formation energy of the LnPc2+SWCNT hybrid depends on the metal atom and the nanotube chirality. LaPc2 and LuPc2 bind stronger to the zigzag nanotube, while for GdPc2, bonding to the armchair nanotube is the stronger one. The HOMO-LUMO gap energy (Egap) shows a correlation between the nature of lanthanide and the nanotube chirality. In the case of adsorption on armchair nanotube, Egap tends to match the gap of isolated LnPc2, whereas for adsorption on the zigzag nanotube, it is closer to the value for the isolated nanotube model. The spin density is localized on the phthalocyanines ligands (plus on Gd in the case of GdPc2), when the bisphthalocyanine is adsorbed on the surface of the armchair nanotube. For bonding to zigzag nanotube (ZNT), it extends over both components, except for LaPc2+ZNT, where spin density is found on the nanotube only. Method All DFT calculations were carried out using the DMol3 module of Material Studio 8.0 software package from Accelrys Inc. The computational technique chosen was the general gradient approximation functional PBE in combination with a long-range dispersion correction developed by Grimme (PBE-D2), the double numerical basis set DN, and the DFT semi-core pseudopotentials.
Teses / dissertações sobre o assunto "Modèle pseudopotential"
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Koyeerath, Graham Danny. "Topology optimization in interfacial flows using the pseudopotential model". Electronic Thesis or Diss., Nantes Université, 2024. http://www.theses.fr/2024NANU4008.
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L'optimisation des systèmes et des processus est un exercice qui s'effectue en tenant compte de l'expérience et des connaissances de chacun. Nous explorons ici une approche mathématique pour optimiser les problèmes physiques en utilisant divers algorithmes d'optimisation. Dans cette thèse, l'objectif préliminaire de l'optimiseur est de modifier les caractéristiques d'écoulement du système en ajustant les forces capillaires. Cet objectif peut être atteint en modifiant l'un des deux ensembles de paramètres : (a) en introduisant un matériau solide mouillant (paramètre de niveau) ou (b) en changeant la mouillabilité des surfaces solides existantes (paramètre de mouillabilité). Nous proposons que le premier ensemble de paramètres soit modifié à l'aide de l'algorithme d'optimisation topologique, où le gradient de la fonction de coût est obtenu en résolvant un modèle d'état adjoint pour le modèle monocomposant multiphase de Shan et Chen (SCMP-SC). De même, nous proposons que ce dernier ensemble de paramètres soit modifié à l'aide de l'algorithme d'optimisation de la mouillabilité, où nous dérivons à nouveau un modèle d'état adjoint pour le modèle SCMPSC. Enfin, nous utilisons un algorithme d'optimisation multi-échelle, dans lequel nous calculons le gradient de la fonction de coût à l'aide de la différence finie. Nous avons réussi à démontrer la compétence de cet optimiseur pour maximiser la vitesse moyenne d'une gouttelette 2D jusqu'à 69%The optimization of systems and processes is an exercise that is carried out taking into account one’s experience and knowledge. Here we explore a mathematical approach to optimize physical problems by utilizing various optimization algorithms. In this thesis, the preliminary objective of the optimizer is to modify the flow characteristics of the system by tweaking the capillary forces. This could be accomplished by modifying either of the two sets of parameters: (a) by introducing a wetting solid material i.e. the level-set parameter or (b) by changing the wettability of the existing solid surfaces i.e. the wettability parameter. We propose that the former set of parameters could be modified using the topology optimization algorithm, where the gradient of the cost function is obtained by solving an adjointstate state model for the single component multiphase Shan and Chen (SCMP-SC) model. Similarly, we propose that the latter set of parameters are modified using the wettability optimization algorithm where we again derive an adjoint-state model for the SCMP-SC. Lastly, we utilize a multiscale optimization algorithm, where we compute the gradient of the cost function using the finite difference. We have succeeded in demonstrating the competence of this optimizer for maximizing the mean velocity of a 2D droplet by up to 69%
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Silva, Maurício Chagas da. "Estudo teórico de efeitos de solvatação do tetraidrofurano sobre um mecanismo modelo de Suzuki-Miyaura". [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/248953.
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Orientador: Nelson Henrique MorgonTese (doutorado) - Universidade Estadual de Campinas, Instituto de Química
Made available in DSpace on 2018-08-18T09:48:03Z (GMT). No. of bitstreams: 1 Silva_MauricioChagasda_D.pdf: 1640271 bytes, checksum: 4dc0aa6f7b350fe3e8808a9095aba5fe (MD5) Previous issue date: 2011
Resumo: Utilizando a implementação do método da coordenada geradora discretizada nos orbitais atômicos, conjuntos de bases adaptados ao pseudopotencial de caroço SBKJC (conjuntos GBSMCS) foram desenvolvidos, validados e utilizados no estudo de possíveis efeitos de solvatação do tetraidrofurano sobre um mecanismo modelo de Suzuki-Miyaura. As metodologias de validação adotadas para os conjuntos GBSMCS foram os cálculos teóricos da afinidade por próton de sistemas atômicos e moleculares, iônicos e neutros, das entalpias de liquefação de alguns solventes orgânicos rotineiros e das entalpias de hidratação de 29 compostos orgânicos diversos. Nas etapas de validação, observou-se de uma maneira geral, uma boa relação entre custo e benefício na utilização dos conjuntos de bases GBSMCS, obteveram-se desvios médios por volta de 0 até 20 kJ.mol, nas propriedades estudadas. Com as metodologias propostas neste trabalho e com a utilização dos conjuntos GBSMCS, determinou-se o perfil potencial da reação modelo de Suzuki-Miyaura tanto em fase gasosa como em fase solvatada de tetraidrofurano. Não se observou efeitos significativos nas estruturas dos estados estacionários caracterizados e nem nas DrG para as etapas de adição-oxidativa, transmetalação, eliminação-redutiva e isomerização. Contudo, observou-se que há efeitos consideráveis de solvatação para as espécies individuais. As etapas de adição-oxidativa e de eliminação-redutiva apresentaram-se como sendo etapas exergônicas e a etapa de transmetalação como sendo uma etapa endergônica tanto em fase gasosa como em tetraidrofurano. Abordou-se um mecanismo associativo em todas as etapas principais reacionais, contudo inferiu-se que a etapa de transmetalação tenha possíveis rotas mecanísticas dissociativas iônicas que serão estudadas em trabalhos futuros
Abstract: Using the implementation of the discretized generator coordinate method in atomic orbitals, atomic basis sets adapted to the pseudopotential core SBKJC were developed ( GBSMCS ), validated and used to study possible effects of tetrahydrofuran¿s solvation over a model Suzuki-Miyaura¿s mechanism. The methodologies adopted for the validation of GBSMCS basis sets were the theoretical calculations of proton affinities of atomic and molecular, ionic and neutral, systems, the liquefaction enthalpies of some common organic solvents and the hydration enthalpies of 29 organic compounds. In the validation steps a good relationship was abserved between cost and benefit in the use of GBSMCS basis set, average deviations around 0 to 20 kJ.mol for the properties studied. Applying the methodologies proposed in this research and using the GBSMCS atomic basis sets, the potential profile of the Suzuki- Miyaura¿s model mechanism was determinated in the gas and tetrahydrofuran phases. No significant tetrahydronfuran¿s solvation effects were observed for molecular stationarys state structures, neither for DrG for oxidative- addition, transmetallation, reductive-elimination and isomerization reaction steps. However, some strong solvation effects were observed for individual species. The oxidative-addition and reductive-elimination reaction steps were characterized as exergonic steps, but transmetallation reaction step was presented as an endergonic step, both in the gas and tetrahydrofuran phases. This work approaches an associative mechanism for all main reaction steps; however, we inferred that the transmetallation reaction step could have some ionic pathways and should be studied in future works
Doutorado
Físico-Química
Doutor em Ciências
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Citrini, France. "Etude théorique de la double photoionisation des alcalino-terreux". Paris 11, 2002. http://www.theses.fr/2002PA112169.
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Cette thèse est une contribution sur l'étude théorique de la double photoionisation des alcalino-terreux. Le premier chapitre présente les caractéristiques du processus et les principales méthodes utilisées pour le décrire. Pour cela, nous utilisons la méthode Hyperspherical R-matrix with Semi-classical Outgoing Waves (HRM-SOW) qui a été validée pour He. Cette méthode est développée en détail dans le chapitre 2. Comme l'approche HRM-SOW décrit des atomes à deux électrons, il faut ramener les alcalinoterreux à des systèmes biélectroniques. Ceci est possible grâce aux potentiels effectifs de coeur qui modélisent l'interaction entre les électrons de coeur et les électrons de valence. Il faut alors déterminer les fonctions d'onde à deux électrons de l'état fondamental de l'atome, cohérentes avec le potentiel effectif choisi, en utilisant les méthodes standard de calcul de structure électronique. Le chapitre 3 présente ces méthodes ainsi que les différents types de potentiels effectifs de coeur disponibles. Il expose également une technique numérique particulière utilisée par la suite : la méthode des réseaux de Lagrange, appartenant à la famille des méthodes de grille. Le chapitre 4 présente la méthode originale de calcul des fonctions d'onde que nous avons mise au point ainsi que le code associé. Dans le chapitre 5, nous présentons pour Be, Mg, et Ca, les potentiels effectifs utilisés et les fonctions biélectroniques déterminées par ce code. Des résultats préliminaires, obtenus avec la méthode HRM-SOW dans un modèle où les deux électrons sent supposés rester à distance égale du noyau, sont présentés dans le chapitre 6. Le chapitre 7 expose nos résultats les plus avancés pour Be, obtenus avec la version générale de la méthode HRM-SOW où la contrainte est levéeThis thesis is a contribution to the theoretical study of the double photoionisation of alkaline earths. Chapter 1 presents the major features of the process and the main methods that have been used to describe it. For this study, we use the Hyperspherical R-matrix with Semi-classical Outgoing Waves (HRM-SOW) method, that has been recently validated in the case of He. This method is developed in detail in chapter 2. As the HRM-SOW approach is restricted to two-electrons atoms, alkaline earths have to be represented as bielectronic systems. This is possible thanks to effective core potentials which modelise the interaction between core electrons and valence electrons. So, we have to determine two-electrons wavefunctions of the ground states of the various alkaline earths, consistent with the effective potentials chosen, using the standard methods of electronic structure calculations. Chapter 3 presents these methods and the different kind of effective core potentials available. Moreover, it explains a particular numerical technique we use next : the Lagrange mesh method, which belongs to the family of grid methods. Chapter 4 gives the original method of wavefunctions calculation we have elaborated and the associated program. In chapter 5, we present, for Be, Mg and Ca, the effective core potentials used and the wavefunctions determined by the program presented in chapter 4. Preliminary results, obtained with the HRM-SOW method in a model where the two electrons were assumed to stay at equal distances from the nucleus, are presented in chapter 6. The last chapter displays our more advanced results on Be, obtained with the general version of the HRM-SOW method, where this contraint is relaxed
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Metsue, Arnaud. "Modélisation des structures de coeurs des dislocations dans les minéraux du manteau terrestre à l’aide du modèle de Peierls-Nabarro". Thesis, Lille 1, 2010. http://www.theses.fr/2010LIL10001/document.
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La déformation plastique des minéraux des roches mantelliques joue un rôle-clé dans les phénomènes de convection globale à l’intérieur de la Terre. Cependant, les mécanismes de déformation des minéraux sont encore mal compris. Généralement, la déformation plastique est assurée par le mouvement des dislocations qui sont des défauts linéaires du cristal. La mobilité des dislocations est déterminée par la structure de coeur des défauts. Le modèle de Peierls-Nabarro auquel nous avons recours est un concept fondamental qui décrit la résistance qu’oppose le cristal au mouvement des dislocations au travers du calcul de la contrainte de Peierls et qui fournit également l’étalement du coeur de la dislocation dans le cristal. Développé il y a plus d'un demi-siècle, ce modèle connut un regain d’intérêts dans les années 70 avec l’introduction du concept de fautes d’empilement généralisées qui permet une description plus générale des coeurs de dislocations. La détermination de ces fautes consiste à calculer ab initio ou à l’aide de potentiels empiriques des barrières d’énergie associées au cisaillement d’un plan cristallographique donné dans une, deux ou toutes les directions. L’étude menée durant cette thèse s’est portée sur la détermination des structures de coeur des dislocations de la phase post-perovskite présente à la base du manteau mais également de la wadsleyite, de la forsterite et du diopside, trois minéraux majeurs entre la croûte et 520km de profondeur. L’utilisation du modèle de Peierls-Nabarro unidimensionnel dans un premier temps a été étendue aux trois dimensions de l’espace dans le but de modéliser des structures de coeur de dislocations de plus en plus complexesPlastic deformation of minerals in rocks plays an important role in the global convection of the Earth’s mantle. However, the deformation mechanisms of minerals are not well-known. In general, plastic deformation is due to the dislocation motion. The dislocations are linear defects of the crystal. The mobility of the dislocation is governed by the dislocation core structure.Here, we used the Peierls-Nabarro model that is a theoretical model to address the issue of dislocation core modelling. This model provides also the lattice friction of the crystal against the dislocation motion through the calculation of the Peierls stress. Developed more than 50 years, the model has a great interest since the 70’s with the introduction of the generalized stacking fault (GSF) concept that provides a general description of the dislocation core. The determination of the GSF consists in the calculations of energy barriers associated with the shearing of the crystal in a crystallographic plane in one or more directions. In this study, we have determined the dislocation core structures of the post-perovskite phase present at the core-mantle boundary and of the wadsleyite, diopside and forsterite, major minerals from the crust to 510Km deep. We used the one-dimension formulation of the Peierls-Nabarro model in a first time that has been extended to three dimensions in order to model much more complex dislocation cores
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Mouas, Mohamed. "Etude par dynamique moléculaire de la structure atomique et de la compressibilité isotherme de métaux liquides. Calcul de la diffusion et de la viscosité de soudures sans plomb par le formalisme de Green-Kubo". Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0057/document.
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Les propriétés physiques et thermodynamiques des métaux liquides dépendent de la structure électronique. La structure ionique est décrite soit par la fonction de corrélation de paires dans l'espace réel ou par le facteur de structure dans l'espace réciproque. Celui-ci est directement accessible par diffraction de neutrons ou de rayons X. Le formalisme du pseudopotentiel nous permet de construire le potentiel effectif interionique, ce dernier est utilisé dans la simulation par dynamique moléculaire pour étudier les propriétés statiques comme la structure atomique et les propriétés dynamiques comme la diffusion et la viscosité. Les calculs ont été faits pour l'étain liquide, pour les métaux nobles ainsi que pour leurs alliages constituant les soudures sans plomb. Nous décrivons dans le premier chapitre les différentes propriétés des métaux liquides. Dans le chapitre II, nous présentons le formalisme du pseudopotentiel et la méthode de simulation par dynamique moléculaire. Dans le chapitre III, nous testons d'abord différents pseudopotentiels sur l'étain liquide et nous prouvons que le pseudopotentiel de Shaw local est le seul qui décrit d'une manière correcte la structure atomique. On utilise ensuite ce potentiel pour déterminer le coefficient de diffusion à partir de la fonction d'autocorrélation de vitesse et de sa transformée de Fourier: la densité spectrale. La viscosité de cisaillement est enfin calculée, pour la première fois à notre connaissance, pour l'étain liquide en utilisant la formule de Green-Kubo par intégration de la fonction d'autocorrélation des contraintes. Il est aussi particulièrement difficile de décrire correctement les métaux nobles avec la théorie des pseudopotentiels. En effet leur densité d'états est influencée par leur bande d. Pour surmonter cette difficulté, nous associons le concept de valence effective au potentiel de Shaw local. Les facteurs de structure calculés en fonction de la température sont en très bon accord avec les valeurs expérimentales. L'adéquation du choix du pseudopotentiel est confirmée par les résultats des coefficients de diffusion et de viscosités de cisaillement. Les propriétés des métaux purs et des alliages (soudures sans plomb) calculées en fonction de la température sont en bon accord avec les valeurs expérimentales, prouvant que le pseudopotentiel est transférable aux alliages. Cela confirme notre choix initial du pseudopotentiel local de Shaw et l'introduction du concept de valence effective. Une bonne connaissance de la diffusion et de la viscosité est très importante d'un point de vue industriel pour comprendre les problèmes technologiques liés au mouillage des substrats par les soudures et à la formation d'intermétalliques entre les soudures et le substratThe physical and thermodynamical properties of liquid metals depend on the electronic structure. The ionic structure is described either by the pair correlation function in real space or by the structure factor in reciprocal space which is directly accessible by neutrons or X rays diffraction measurements. Pseudopotential formalism allows us to construct an ionic effective potential. It is used in Molecular Dynamics simulation to study the static properties like the atomic structure and the dynamic ones like diffusion and viscosity. These calculations have been done for liquid tin, for noble metals and for theirs alloys forming lead-free solders. We first describe in chapter I the different properties of liquid metals. In chapter II we present the pseudopotential formalism and the Molecular Dynamics method. In chapter III we first test different pseudopotentials on liquid tin and we prove that the Shaw local model potential is the only one able to describe adequately the atomic structure. Then we used it to determine the diffusion coefficient from the velocity autocorrelation function and from its Fourier transform: the spectral density. Finally, we calculated, for the first time to our knowledge, the shear viscosity of liquid tin with Green-Kubo formula by integrating the stress autocorrelation function. It is also particularly difficult to describe correctly liquid noble metals with pseudopotentials since their density of states is influenced by their d band. To overcome this difficulty we associate the concept of effective valence (determined theoretically) to the Shaw local potential. The calculated structure factors as function of temperature are in a very good agreement with the experimental ones. The adequacy of the choice of our pseudopotential is confirmed by the results of diffusion coefficients and shear viscosities. The properties of pure metals and alloys (lead free solders) as function of temperature are in good agreement with experimental values proving that the Shaw local pseudopotential is transferable to alloys. This confirms our initial choice of pseudopotential and effective valence. Having a good knowledge of diffusion and viscosity is very important from an industrial point of view. Indeed, we need understanding technological problems linked to the wetting of a solder on a substrate and to the formation of intermetallics between the solder and the substrate
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Hliwa, Mohamed. "Traitement simplifie des interactions moleculaires en chimie quantique". Toulouse 3, 1988. http://www.theses.fr/1988TOU30038.
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Calculs ab initio sur le systeme hautement degenere cr h: mise en evidence d'un fort couplage entre etats ioniques et neutres et analyse des fonctions d'onde dans une description diabatique. Proposition d'une methode perturbative pour calcul des energies de dispersion entre un systeme versatil a (decrit dans une grande base) et un systeme quasi passif b (traite a l'approximation en coeur gele et caracterise par sa polarisabilite); calcul scf + ci de (a + b gele), du champ electrique exerce par a sur b, et de ses fluctuations, a l'aide d'un hamiltonien effectif; application a l'etude des courbes de potentiel des premiers etats excites des molecules diatomiques de ar avec na, k ou mg. Emploi de la theorie des pseudopotentiels et des potentiels modeles pour le calcul de potentiels impulsifs d'atomes inertes transferables a des systemes moleculaires; a partir de ces potentiels, calcul d'energies de dispersion applicable a la spectroscopie d'atomes alcalins en matiere de gaz rare
Livros sobre o assunto "Modèle pseudopotential"
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Dyall, Kenneth G., e Knut Faegri. Introduction to Relativistic Quantum Chemistry. Oxford University Press, 2007. http://dx.doi.org/10.1093/oso/9780195140866.001.0001.
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This book provides an introduction to the essentials of relativistic effects in quantum chemistry, and a reference work that collects all the major developments in this field. It is designed for the graduate student and the computational chemist with a good background in nonrelativistic theory. In addition to explaining the necessary theory in detail, at a level that the non-expert and the student should readily be able to follow, the book discusses the implementation of the theory and practicalities of its use in calculations. After a brief introduction to classical relativity and electromagnetism, the Dirac equation is presented, and its symmetry, atomic solutions, and interpretation are explored. Four-component molecular methods are then developed: self-consistent field theory and the use of basis sets, double-group and time-reversal symmetry, correlation methods, molecular properties, and an overview of relativistic density functional theory. The emphases in this section are on the basics of relativistic theory and how relativistic theory differs from nonrelativistic theory. Approximate methods are treated next, starting with spin separation in the Dirac equation, and proceeding to the Foldy-Wouthuysen, Douglas-Kroll, and related transformations, Breit-Pauli and direct perturbation theory, regular approximations, matrix approximations, and pseudopotential and model potential methods. For each of these approximations, one-electron operators and many-electron methods are developed, spin-free and spin-orbit operators are presented, and the calculation of electric and magnetic properties is discussed. The treatment of spin-orbit effects with correlation rounds off the presentation of approximate methods. The book concludes with a discussion of the qualitative changes in the picture of structure and bonding that arise from the inclusion of relativity.
Capítulos de livros sobre o assunto "Modèle pseudopotential"
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Chelikowsky, James R. "Pseudopotential methods". In Reference Module in Materials Science and Materials Engineering. Elsevier, 2022. http://dx.doi.org/10.1016/b978-0-323-90800-9.00122-0.
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Dolg, Michael, e Xiaoyan Cao. "Relativistic Pseudopotentials". In Reference Module in Chemistry, Molecular Sciences and Chemical Engineering. Elsevier, 2023. http://dx.doi.org/10.1016/b978-0-12-821978-2.00086-6.
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Moriarty, John A. "Interatomic Potentials in Simple Metals". In Theory and Application of Quantum-Based Interatomic Potentials in Metals and Alloys, 91–134. Oxford University PressOxford, 2023. http://dx.doi.org/10.1093/oso/9780198822172.003.0003.
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Abstract In this chapter, quantum-based interatomic potentials for simple metals are derived starting from the corresponding cohesive-energy functional established in Chapter 2 via density functional theory and pseudopotential perturbation theory. This functional is expressed in reciprocal space for a general nonlocal pseudopotential and then transformed to the desired real-space representation in terms of a volume term and a volume-dependent pair potential. To allow full evaluation of the pseudopotential and the pair potential from first principles, a self-consistent electron screening calculation is also made. Accurate pair potentials so calculated have been obtained for a number of simple metals, including Na, Mg and Al prototypes, using two different optimized forms of nonlocal pseudopotential: the basic Austin, Heine and Sham form employed in generalized pseudopotential theory, and the norm conserving model potential form of Dagens, Rasolt and Taylor. Efficient practical methods to deal with the long-range Friedel oscillations in the pair potential arising from the self-consistent screening are also discussed.
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Schrader, D. M., T. Yoshida e K. Iguchi. "Binding energies of positronium fluoride and positronium bromide by the model potential quantum Monte Carlo method". In Quantum Monte Carlo, 88. Oxford University PressNew York, NY, 2007. http://dx.doi.org/10.1093/oso/9780195310108.003.0091.
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Abstract This paper and a companion paper0 describe three pseudopotential QMC calculations for the positronium halides PsF, PsCl, and PsBr with accuracies and reliabilities not previously available. These three compounds have a fleeting lifetime sufficiently long that time-independent nonrelativistic quantum mechanics should give good estimates of their energies but too short to allow direct measurements of those energies. Earlier estimates of several types and calculations at the Hartree-Fock level had given a wide spread in predictions of the binding energies of positronium to the halide ions, mostly in the range of 1 to 3 eV for the three molecules. The calculations were fixed-node diffusion QMC calculations for the eight valence electrons and the positron with a model potential expression replacing the core electrons and halide nucleus. The model or pseudopotential used was a simplified version without valence-core correlation and with several lesser terms eliminated in order to make it a local pseudopotential. This modelb had been used previously in successful predictions of the electron affinity of the Cl atom. An importance sampling trial wavefunction was constructed of Hartree-Fock orbitals for the halide ion and a 2s orbital for the positron, along with an electron-positron term but no electron-electron correlation terms. Checks of the consistency of the calculations with independent estimates of the correlation energies were entirely satisfactory. The results, in terms of binding energies, were obtained in the range of 1-2 eV (with uncertainties of 0.1-0.2 eV) in an order consistent with competitive formation experiments.
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Igor, Vurgaftman. "Methods for Computing the States of Quantum Structures". In Bands and Photons in III-V Semiconductor Quantum Structures, 271–302. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198767275.003.0009.
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This chapter presents a detailed development of several numerical methods for calculating the band structure of semiconductor quantum wells and superlattices. These include the transfer-matrix method, the finite-difference method, and the reciprocal-space approach. The relative merits and drawbacks of each approach are briefly considered. It is pointed out that real-space methods often introduce spurious states for the most common forms of the Hamiltonian. The chapter also discusses how the tight-binding and pseudopotential methods can be applied to model quantum structures.
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Schautz, F., e H. J. Flad. "Selective correlation scheme within diffusion quantum Monte Carlo". In Quantum Monte Carlo, 135. Oxford University PressNew York, NY, 2007. http://dx.doi.org/10.1093/oso/9780195310108.003.00138.
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Abstract This paper describes the development of a new scheme for using an effective model potential to reduce the number of electrons explicitly treated in a QMC calculation for a molecular system. Like other pseudopotential and model-potential approaches it is based on differing treatments of core and valence (or frozen and explicitly correlated) electrons. It differs from the earlier schemes of Yoshida and co-workers0 in that it is adapted to multicenter systems and includes a projectionlike operator to enforce orthogonality between orbitals for the two sets of electrons. The model potential includes Coulomb and exchange terms and the projectionlike operator. The latter two are nonlocal. For these a localization procedure, similar to those used in pseudopotential calculations, was derived. In implementing the scheme the authors had to explore a number of questions, such as those related to nonequivalent nodal domains, and to devise a number of approximations to simplify the calculations. The triple-bonded nitrogen molecule N2, with correlation for the electrons of the bonding orgitals and with the nonbonding orbitals frozen, was used as a test case. A coupled cluster [CCSD(T)] calculation with a large basis set provided a benchmark with a correlation energy of 228 mhartree for the triple bond estimated to be accurate within a few mhartree. The corresponding result for the QMC calculation using the best approximations differed by 2-6 mhartree. Thus, quantitative agreement was obtained within the limits of statistical error. The authors indicated a “good chance” for further development to enable efficient treatment of problems involving solids and surfaces.
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Moriarty, John A. "High-Temperature Properties, Melting and Phase Diagrams". In Theory and Application of Quantum-Based Interatomic Potentials in Metals and Alloys, 336–81. Oxford University PressOxford, 2023. http://dx.doi.org/10.1093/oso/9780198822172.003.0008.
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Abstract In this chapter, the treatment of thermodynamic properties, phase stability and phase transitions in metals via quantum-based interatomic potentials (QBIPs) is extended to high temperature (high T), including anharmonic vibrational effects in the solid, liquid-state structure and energetics and pressure-temperature phase diagrams. In addition to standard molecular dynamics (MD) techniques, the tools of reversible-scaling MD and variational perturbation theory are introduced to obtain accurate solid and liquid free energies. Respective pair and multi-ion QBIPs from generalized pseudopotential theory (GPT) for the simple metal Mg and from model-GPT for the transition metal Ta are used to illustrate a wide range of high-T solid and liquid applications of interest at both ambient pressure and high pressure. These applications include calculations of the specific heat, thermal expansion coefficient, elastic moduli, shock Hugoniot and melt curve, with detailed comparison to experiment. Also discussed in the case of Ta are large-scale MD simulations of rapid solidification and high-T solid polymorphism.
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Moriarty, John A. "Structural Phase Stability and High-Pressure Phase Transitions". In Theory and Application of Quantum-Based Interatomic Potentials in Metals and Alloys, 253–81. Oxford University PressOxford, 2023. http://dx.doi.org/10.1093/oso/9780198822172.003.0006.
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Abstract In this chapter, we address the subject of structural phase stability in both nontransition and transition metals, including as a fundamental test of prototype quantum-based interatomic potentials, calculation of the ground-state crystal structure amongst various competing alternate structures. In this process, we also discuss: (i) the basic separation of cohesion and structure in generalized pseudopotential theory (GPT); (ii) total-energy variations along important deformation paths connecting different higher-energy structures, including the Bain path linking the bcc and fcc structures; and (iii) structural phase stability in metals across the Periodic Table; and (iv) the prediction of pressure-induced solid-solid phase transitions, including a number of noteworthy GPT and model-GPT predictions that were subsequently confirmed by experiment.
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Yoshida, T., e G. Miyako. "Quantum Monte Carlo with model potentials for molecules". In Quantum Monte Carlo, 111. Oxford University PressNew York, NY, 2007. http://dx.doi.org/10.1093/oso/9780195310108.003.00114.
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Abstract Although simple model potentials lack the solid theoretical basis that justifies nonlocal pseudopotentials, they have been used with moderate success in replacing the core electrons in analytic variational calculations and in diffusion QMC calculations. For this paper, a model potential of long standing, proposed by Bonifacic and Huzinagaa in 1974, was investigated in calculations of dissociation energies for the molecules CO, HCl, Na2, and K2, The model potential has an especially simple form for the effective field of the core electrons based on core orbitals. The valence electrons are treated explicitly with Hartree-Fock orbitals used in determinantal trial functions for importance sampling and node location. The numbers of valence electrons treated were: CO, 10; HCl, 8; Na2, 2; K2, 2. In each case, the calculated dissociation energy was found to be accurate to within a few percent of the experimental value and much more accurate than either all-electron or model-potential Hartree-Fock calculations. Despite concerns about its justification, the method appears to be surprisingly successful.
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Moriarty, John A. "Defects and Mechanical Properties". In Theory and Application of Quantum-Based Interatomic Potentials in Metals and Alloys, 382–424. Oxford University PressOxford, 2023. http://dx.doi.org/10.1093/oso/9780198822172.003.0009.
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Abstract This chapter treats the important subject of defects in metals, including vacancies, interstitials, dislocations and grain boundaries. All of these defects, in addition to the bulk elasticity that underpins them, are impacted by quantum mechanics, again confirming the fundamental importance of quantum-based interatomic potentials. The discussion here is mainly focused on the bcc transition metals, where extensive applications have been made using model generalized pseudopotential theory. Calculations of point defect formation and migration energies, ideal shear strength and generalized stacking fault energy surfaces compare favorably with density functional theory results. A special Green’s function method is used to study screw dislocation core structure and mobility, including kink-pair energetics and the Peierls stress. Multiscale modeling of crystal plasticity and strength in Ta and Mo is then made possible via dislocation mobility input into micron-scale dislocation dynamics simulations. Predictions of grain-boundary structure in Nb, Mo and Ta have also been validated by experiment.
Trabalhos de conferências sobre o assunto "Modèle pseudopotential"
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De la Torre Pari, S. A., F. F. H. Aragón, L. Villegas-Lelovsky e D. G. Pacheco Salazar. "A DFT study of structural and electronic properties of anatase TiO2 phase with Ni and oxygen vacancies impurities". In VIII Simpósio de Estrutura Eletrônica e Dinâmica Molecular. Universidade de Brasília, 2020. http://dx.doi.org/10.21826/viiiseedmol2020136.
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In the present work, first-principle theory using the functional density theory (DFT) was used in the ABINIT software package using the PBE pseudopotential (norm-conserving pseudopotentials). To determine the structural parameters such as lattice constant, Bulk modules, and energy formation, for the TiO2 anatase phase doped with substitutional and interstitial nickel impurity, oxygen vacancies (VO) are also included in the present work. For this study, the 2x1x1 supercells with 24 atoms and 2x2x1 with 48 atoms were used. Different types of Ni dopants and oxygen vacancies were considered for energy formation using the 2x2x1 supercell. Our results show that the values of network parameters, minimum energy, and Bulk modulus remain constant with the supercell's growth. With the inclusion of Ni in the supercell substituting the Ti-ions, the unit cell volume (V) exhibits a decrease in agreement with ionic radii mismatch between Ti and Ni atoms. However, when entry as an interstitial form a significant increase is shown. The preliminary results of the energy of formation analyzed for the Ni defects show that it is more probable for an interstitial Ni than for a substitutional Ni.
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De la Torre Pari, S. A., F. F. H. Aragón, L. Villegas-Lelovsky e D. G. Pacheco Salazar. "A DFT study of structural and electronic properties of anatase TiO2 phase with Ni and oxygen vacancies impurities". In VIII Simpósio de Estrutura Eletrônica e Dinâmica Molecular. Universidade de Brasília, 2020. http://dx.doi.org/10.21826/viiiseedmol2020106.
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In the present work, first-principle theory using the functional density theory (DFT) was used in the ABINIT software package using the PBE pseudopotential (norm-conserving pseudopotentials). To determine the structural parameters such as lattice constant, Bulk modules, and energy formation, for the TiO2 anatase phase doped with substitutional and interstitial nickel impurity, oxygen vacancies (VO) are also included in the present work. For this study, the 2x1x1 supercells with 24 atoms and 2x2x1 with 48 atoms were used. Different types of Ni dopants and oxygen vacancies were considered for energy formation using the 2x2x1 supercell. Our results show that the values of network parameters, minimum energy, and Bulk modulus remain constant with the supercell's growth. With the inclusion of Ni in the supercell substituting the Ti-ions, the unit cell volume (V) exhibits a decrease in agreement with ionic radii mismatch between Ti and Ni atoms. However, when entry as an interstitial form a significant increase is shown. The preliminary results of the energy of formation analyzed for the Ni defects show that it is more probable for an interstitial Ni than for a substitutional Ni.
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Nabavizadeh, Seyed Amin, Mohsen Eshraghi e Sergio D. Felicelli. "Feasibility Study of Different Pseudopotential Multiphase Lattice Boltzmann Methods for Dendritic Solidification". In ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-71019.
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The formation of porosity and bubbles during solidification in manufacturing processes like casting or welding of metals has a negative effect on the mechanical properties of the manufactured components. Numerical simulation of this problem is important since the direct observation of the interaction of bubbles with dendrites is limited by the opacity of metals. Therefore, developing a reliable numerical model is essential to predict the mechanical properties of materials after solidification. The pseudopotential multiphase model is a popular method for simulating multiphase flow using the lattice Boltzmann method. This model and its variations have been used to simulate a variety of problems successfully. However, the original pseudopotential model has some deficiencies, including large spurious current and restriction to model low density and viscosity ratios. Several schemes have been proposed to improve the pseudopotential multiphase model and overcome the limitations, including using a realistic equation of state, introducing a force with higher order of isotropy, introducing a middle-range repulsion force, and implementing the force similarly to the Exact Difference Method (EDM). The aim of this article is to investigate these various enhancements available for the pseudopotential multiphase model in order to come up with a reliable scheme to simulate motion and interaction of bubbles during dendritic solidification in binary alloys. The proposed model is validated against published literature.
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Tang, Jun, Shengyuan Zhang e Huiying Wu. "Three-Dimensional Weighted Multiple-Relaxation-Time Pseudopotential Lattice Boltzmann Method for Multiphase Flow". In ASME 2021 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/fedsm2021-65506.
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Abstract The pseudopotential lattice Boltzmann (LB) method has been widely used for simulating multiphase flow due to its concise concept and computational simplicity. In this paper, based on the weighted orthogonal transformation matrix, a three-dimensional (3D) weighted multiple-relaxation-time pseudopotential lattice Boltzmann method (WRMT-LBM) is developed, in which the standard lattice stencil D3Q19 is adopted. Compared with the classical multiple-relaxation-time pseudopotential lattice Boltzmann method (CMRT-LBM) based on the orthogonal transformation matrix, the expressions of the equilibrium density distribution function and discrete force term in moment space are simplified in the present model, which contributes to simplifying the program implementation and improving the computational efficiency. Moreover, an additional discrete source term in moment space compatible with the proposed model is introduced to achieve tunable surface tension. A series of numerical tests are then implemented to investigate the performance of the proposed model. Compared with the CMRT-LBM, the results of the present model can achieve lower spurious velocity and higher computational efficiency while keeping comparable accuracy. Furthermore, using the present model, three benchmark cases, including droplet oscillation, droplet impacting on wall and droplet impact on thin film, are performed to investigate the performance of this model. The numerical results are in good agreement with the analytical solutions or the empirical correlations in the literature, which demonstrates that the present model can simulate the multiphase flow with large density ratio.
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Zunger, Alex. "Pseudopotential Theory of Semiconductor Quantum Dots, Wires and Films". In Chemistry and Physics of Small-Scale Structures. Washington, D.C.: Optica Publishing Group, 1997. http://dx.doi.org/10.1364/cps.1997.ctua.4.
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The electronic structure of nanostructures has been almost universally addressed by the “standard model” of effective-mass k·p envelope function approach. While eminently successful for quantum wells, this model breaks down for small structures, in particular, for small dots and wires[l]. Until recently, it was impractical to test the “standard model” against more general approaches that allow many-band (Γ-X-L) coupling. However, it is now possible, due to special tricks[2], to apply the all-band pseudopotential method to 103 - 104 atom nanostructures. This shows (i) how the “standard model” fails, for thin superlattices, [3], (ii) how size effect lead to a reduction in dielectric constants[3] and to band gaps that differ from what is expected in effective-mass theory, (iii) the emergence of a “zero-confinement state” in 2D films [4], (iv) that small dots of III-V materials have an indirect gap that converts to direct above a critical size[5], (v) how the spectra of CdSe dots evolve from the bulk[6] and (vi) how the spectra of dots of Si, GaAs, InP and CdSe compare with experiment, and (vii) how the use of pseudopotential wavefunctions leads to very different electron-hole coulomb and exchange energies relative to the “standard model”.
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Zhao, Wandong, Ben Xu e Ying Zhang. "Three-Dimensional Multiple-Relaxation-Time Lattice Boltzmann Simulation of Vapor Condensation on Subcooled Wall". In ASME 2018 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/imece2018-88490.
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Oscillating flows and multiphase heat transfer processes frequently occur in many engineering and scientific applications and systems, as is the case in enhanced geothermal energy, CO2 sequestration and storage, and in evaporation in soil, to name a few. Nevertheless, modeling of such flows is a rather challenging task due to the complex interfacial dynamics among different phases and solid porous structures. Over the decades, several types of Lattice Boltzmann (LB) models for multiphase flows have been developed under different physical pictures, for example the color-gradient model, Single-Relaxation-Time (SRT) pseudopotential model, and the HSD model. In this study, a pseudopotential Multiple-Relaxation-Time (MRT) LBM simulation will be utilized to simulate incompressible oscillating flow and condensation in 2D porous media. Initially, the model will be used to optimize the porous structure in order to have the maximum condensation rate of water vapor. Subsequently, the effects of contacting angle, wettability, oscillating frequency and phase angle to the heat flux, the temperature field of porous media, and the condensation rate will be discussed. Moreover, a multiscale approach will be considered in order to couple the heat transfer in macroscale applications. It is expected that such an approach will provide a different perspective regarding the engineering applications involved with oscillating flow and multiphase heat transfer processes.
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Li, Xi, Huixiong Li e Xiaoyi Wu. "Numerical Study of Pool Boiling Heat Transfer on a Heated Cylinder by Lattice Boltzmann Method". In ASME 2024 7th International Conference on Micro/Nanoscale Heat and Mass Transfer. American Society of Mechanical Engineers, 2024. http://dx.doi.org/10.1115/mnhmt2024-131778.
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Abstract Pool boiling is widely utilized in various industrial applications due to the high heat transfer performance. In the numerical simulations, the pseudopotential LB model is capable of simulating the entire boiling processes, including the bubble nucleation. Under the effect of gravity and surface tension, the distribution of phase fields on the circle surface is nonuniform. The bubble dynamics, and the heat transfer characteristics during the pool boiling processes on the circular surfaces would be unique compared to those on the heated plate. In this study, the bubble dynamics and heat transfer during pool boiling processes at a heated cylinder with different wall superheats were simulated using the MRT pseudopotential model coupled with phase-change model. The bubble dynamics and heat transfer with various orientations of the heated cylinder during pool boiling processes were investigated. In addition, the influence of surface tension and saturated temperature on pool boiling heat transfer was studied. It was found that increasing surface tension could enhance the heat transfer performance for the nucleate boiling with high wall superheat, and CHF is proportional to 0.254 power of surface tension. When Ja is low, the saturated temperature has little influence on heat transfer performance. However, in the nucleate boiling regime with large Ja, heat transfer performance as well as CHF decrease with the increasing saturated temperature.
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Carlos-Chilo, A. F., F. F. H. Aragon, L. Villegas-Lelovsky e D. G. Pacheco-Salazar. "Ab-initio Calculations of Structural Parameters, Band Structure and Density of States of Delafossite CuAlO". In VIII Simpósio de Estrutura Eletrônica e Dinâmica Molecular. Universidade de Brasília, 2020. http://dx.doi.org/10.21826/viiiseedmol2020143.
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Delafossite CuAlO2 is a p-type transparent semiconductor oxide with space group R-3m (N°166) is a material with extended applications in different fields. Structural parameters, band structure, and density of CuAlO2 have been investigated in the light of the Density Functional Theory (DFT) using PBE pseudopotentials (norm-conserving pseudopotentials). Our calculations are performed with the ABINIT package using cut-off energy of 100 Hartree, showing convergence to cut-off energy up to 30 Hartree. The lattice parameters of CuAlO2 obtained after the relaxation process are a = b = 2.904 Å and c = 17.202 Å; and consequently, volume of V=174.014 Å3 , also the derivate of the bulk modules Bo´=4.1, and bulk modulus Bo=174 Gpa were found. We find that discrepancies between our calculated lattice parameters a, c, and c/a are overestimated about 0.798%, 0.591%, and 0.219% compared to the reference’s theoretical calculations of Qi-Jun Liu et,al respectively. The calculated energy band structure of CuAlO2 and the high-symmetry points of Brillouin Zone show that the delafossite structure has an indirect band gag (~ 1.21 eV) because the top valence and the bottom conduction are found at F point and Г point, respectively. This work aims to study structural parameters, band structure, and density of states of delafossite CuAlO2 and give one application as solar cell.
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Zhao, Wandong, Ben Xu e Ying Zhang. "Numerical Simulation of Oscillating Multiphase Heat Transfer in Parallel Plates Using Pseudopotential Multiple-Relaxation-Time Lattice Boltzmann Method". In ASME 2018 Power Conference collocated with the ASME 2018 12th International Conference on Energy Sustainability and the ASME 2018 Nuclear Forum. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/power2018-7544.
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Multiphase flows frequently occur in many important engineering and scientific applications, but modeling of such flows is a rather challenging task due to complex interfacial dynamics between different phases, let alone if the flow is oscillating in the porous media. Using humid air as the working fluid in the thermoacoustic refrigerator is one of the research focus to improve the thermoacoustic performance, but the corresponding effect is the condensation of humid air in the thermal stack. Due to the small sized spacing of thermal stack and the need to explore the detailed condensation process in oscillating flow, a mesoscale numerical approach need to be developed. Over the decades, several types of Lattice Boltzmann (LB) models for multiphase flows have been developed under different physical pictures, for example the color-gradient model, the Shan-Chen model, the nonideal pressure tensor model and the HSD model. In the current study, a pseudopotential Multiple-Relaxation-Time (MRT) LBM simulation was utilized to simulate the incompressible oscillating flow and condensation in parallel plates. In the initial stage of condensation, the oscillating flow benefits to accumulate the saturated vapor at the exit regions, and the velocity vector of saturated vapor clearly showed the flow over the droplets. It was also concluded that if the condensate can be removed out from the parallel plates, the oscillating flow and condensation will continuously feed the cold surface to form more water droplets. The effect of wettability to the condensation was discussed, and it turned out that by increasing the wettability, the saturated water vapor was easier to condense on the cold walls, and the distance between each pair of droplets was also strongly affected by the wettability. It’s expected that this study can be used to optimize and redesign the structure of thermal stack in order to produce more condensed water, also this multiphase approach can be extended to more complicated 3D structures.
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Biermann, Mark L., e C. R. Stroud. "Wave packets in a semiconductor superlattice". In Integrated Photonics Research. Washington, D.C.: Optica Publishing Group, 1991. http://dx.doi.org/10.1364/ipr.1991.thf4.
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When a short laser pulse excites a quantum system, a spatially localized wave packet is formed.1 In this paper, we present a theoretical study of hole wave packets in a room temperature semiconductor superlattice, the unit cell of which consists of four layers. The first and third layers are GaAs wells of width 9 and 14 monolayers, 25.4 and 39.6 A. The second and fourth are 5 monolayers, 14.1-Å thick Al0.3Ga0.7As barriers. Effectively, the material is a series of coupled quantum wells of alternating thicknesses. These parameters give an even splitting between the first three hole states. The bandgap discontinuity is split, with 43% allotted to the valence band, and the growth direction is 100. The theoretical model is a k.p. local pseudopotential method based on that of Smith and Mailhiot.2
Relatórios de organizações sobre o assunto "Modèle pseudopotential"
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Straub, G., e J. Wills. Elastic moduli of copper: Electronic structure contributions from pseudopotentials and full-potential linear muffin-tin orbital band structure calculations. Office of Scientific and Technical Information (OSTI), novembro de 1989. http://dx.doi.org/10.2172/5309013.
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